Delivery of drugs to the systemic blood of a patient by means of an electrophoretic/electro-osmotic transdermal system is generally accomplished primarily through the sweat and sebaceous ducts and their respective glands. Some delivery is made through the stratum cornum, or horny layer. The stratum cornum, although very thin, is resistant to the passage of both electrical current and of liquids. The skin ducts cover an area of about one-thousandth of the stratum cornum.
The drug delivery system of my patent application entitled "Transdermal Drug Delivery System", Ser. No. 028679, filed Mar. 20, 1987, describes a semi-dry drug patch and a selected current level delivered to the semi-dry patch that combine to limit liquid containing a drug from moving from the patch to the skin through the sweat and sebaceous ducts so as to starve the skin ducts of liquid and divert the current and the electro-osmotic delivery of the drug through the stratum cornum. A replenishment of the skin ducts with liquid occurs at periodic intervals by an electro-osmotic delivery of the drug solution through the skin ducts. An electrical oscillator can be added to the system so as to apply periodic current increases or pulsations in order to evacuate the skin ducts of water at intervals thus removing these electrical shunts from the delivery system.
The skin of a human is of the type having skin ducts, a type which is common to certain animals such as a horse, and so differs from the skins of animals not having skin ducts, such as a rabbit. Nevertheless, the human skin also has characteristics taken in toto, not only separate duct and stratum cornum characteristics, and therefore can be considered as a unitary cell membrane.
An article that discusses electro-osmotic processes of living membranes is "Electrokinetic Membrane Processes in Relation to Properties of Excitable Tissues" by Torsten Teorell, published in Journal of General Physiology, 1959, Vol. 42, No. 4. A constant electrical current of a first value was applied to a porous, charged membrane corresponding to an excitable cell membrane. The result was a repetitive oscillatory process wherein the membrane at first periodically increased and decreased in resistance over approximate half-hour time periods in what the author described as oscillations. The decreased level of cell membrane resistance corresponded to oscillatory streaming of water solution across the cell membrane. The repetitive oscillations dampened after about an hour and about three oscillations. When a constant electrical current of a second value slightly greater than the first current value was applied to the same membrane, the repetitive oscillations became undamped, that is, the oscillations continued at about half-hour (in fact, slightly less) periods as long as the higher current continued to be applied. The "constant" electrical current in fact naturally increased and decreased in response to lower and higher resistance states of the membrane.
Two different types of drugs, or therapeutic compounds, can be delivered to the body. The therapeutic compound can be either a first type that corresponds to a naturally released body compound, such as a hormone as insulin, or a second type that is foreign to the body, such as nitroglycerin, a cardiovascular drug, an oncological drug, and an analgesic drug.
It is a phenomenon of many therapeutic compounds of the first type that when they are delivered to the systemic blood of the patient in an oscillatory, or pulsating mode, two different effects will occur depending upon the frequency of the drug delivery time relative to the natural delivery rhythm of the body. If a therapeutic compound of the first type is delivered in periodic variations which are applied in similar rhythms as the natural delivery rhythms of the body, the activity of the naturally released body compound will be simulated. If such a therapeutic compound is delivered in periodic electrical variations which are applied more often than the natural delivery rhythms of the body, the natural activity of the body compound will be inhibited or extinguished.
It is also a phenomenon of many therapeutic compounds of the second type that when they are delivered to the systemic blood of the patient in an oscillatory mode as compared to a steady state mode of delivery, a different effect on the patient occurs as compared to the steady state mode. The oscillatory mode is selected in accordance with body requirements.
An example of a therapeutic compound of the first type that corresponds to a natural compound of the body is luteinising hormone-releasing hormone, or LHRH, which is also known as a gonadotrophin releasing hormone, or GnRH, and which controls production of testosterone in males and the inducement of ovulation in females. LHRH is released in accordance with the natural rhythm of the body for approximately 6 minutes every hour. A transdermal drug delivery system that delivers LHRH in a steady state mode or at a different frequency from the natural frequency extinguishes gonadotrophic secretion: That is, the production of either testosterone in males or ovulation in females ceases. On the other hand, a transdermal delivery system that delivers LHRH in a correct pulsating mode in accordance with the natural rhythm of the body simulates, or ensures, the mentioned processes. A natural compound of the body such as LHRH is released in accordance with a natural release rhythm of the body. In the case of LHRH and many other natural compounds there exist active analogues that have certain advantages over the particular natural compound. These active analogues are often used rather than the natural compounds to trigger or to inhibit or extinguish body responses.
An example of a drug of the second type that is foreign to the body is nitroglycerin. It is known that the steady state delivery of nitroglycerin to a heart patient via a transdermal drug delivery system results in a build-up of a tolerance to the drug by the body of the patient in less than 24 hours so that the drug is rendered useless for the 24-hour prophylaxis of stable angina pectoris. This matter is discussed in a paper entitled "Transdermal Nitroglycerin Patches in Angina Pectoris" by Udho Thadani et al., published in "Annals of Internal Medicine", October 1986, Vol. 105, No. 4.
It is known that a pulsating electrical current can be applied to an electrical circuit by various means, for example, by an oscillator in the circuit. Pulsations of potential or current in an electrophoretic drug delivery system that are timed in accordance with an interplay of driving forces present in the drug delivery system including the skin as a transmembrane can accomplish timed drug deliveries that are more precise, reliable, and efficient than with delivery being made by the natural undamped rhythmical variations of the transmembrane potential and resistance caused by a selected steady state electrical current applied to the system. The term pulsation as used herein is a periodic increase or decrease of a quantity, with the quantity herein having reference to the quantity of either potential or current or amount of a liquid with a drug transported across the transdermal skin membrane.
In general, the present invention is applicable to drug delivery systems which involve drugs or therapeutic compounds whose delivery is dependent upon timing, quantity, and direction of current flow.
It is an object of this invention to provide an electrophoretic/electro-osmotic transdermal drug delivery system that rhythmically delivers a therapeutic compound, or drug, to the systemic blood of a patient in response to application of current pulsations to the system which is otherwise devoid of current.
It is another object of this invention to provide an electrophoretic/electro-osmotic transdermal drug delivery system that rhythmically delivers a therapeutic compound to the systemic blood of a patient by application of positive current pulsations with a negative current being alternately applied to the system.
It is another object of this invention to provide an electrophoretic/electro-osmotic transdermal drug delivery system that rhythmically delivers a therapeutic compound to the systemic blood of a patient by application of negative current pulsations with a positive current being alternately applied to the system.
It is another object of this invention to provide an electrophoretic/electro-osmotic transdermal drug delivery system that rhythmically delivers a therapeutic compound to the systemic blood of a patient by application of positive current pulsations with a different positive current being alternately applied to the system.
It is another object of this invention to provide an electrophoretic/electro-osmotic transdermal drug delivery system that rhythmically delivers a therapeutic compound to the systemic blood of a patient by application of negative current pulsations with a different negative current being alternately applied to the system.
It is another object of this invention to provide an electrophoretic/electro-osmotic transdermal drug delivery system that rhythmically delivers a therapeutic compound to the systemic blood of a patient by application of current pulsations so as to reinforce the natural delivery rhythms of the body.
It is another object of this invention to provide an electrophoretic/electro-osmotic transdermal drug delivery system that rhythmically delivers a therapeutic compound to the systemic blood of a patient by application of current pulsations so as to inhibit or negate the natural delivery rhythms of the body.
In accordance with these and other objects there is described herein an electrophoretic/electro-osmotic transdermal drug delivery system for passing at least one therapeutic compound through the skin membrane of a patient by way of a drug patch for delivery to the systemic blood of a patient in selected, periodic pulsations. The system can be varied to accommodate various types of therapeutic compounds having varied characteristics and purposes. The system includes a current oscillator that applies periodic electrical variations to the system in order to trigger rhythmical variations of the potential and resistance of the skin membrane in synchronization with the oscillator so as to cause oscillatory electro-osmotic streaming of the liquid with the therapeutic compound across the skin membrane to the systemic blood of the patient in response to the rhythmical variations. The oscillator causes the power source to deliver a periodic pulsating current that alternates with periods of no current in the system or that alternates with periods of a different current than the pulsating current. The pulsating current can be applied for relatively short periods relative the periods of non-current or the periods of different current or can be applied for long periods relative the periods of non-current of the periods of different current. The different current can be either positive or negative current. During the periods of negative current the liquid with the therapeutic compound tends to be drawn from the skin membrane into the drug patch.